Swap Data Explorer node-type picker to the virtualized Combobox

## Parent

- Part of #2086

## What to build

Swap the Data Explorer **node-type picker** from `SelectField` to the virtualized searchable Combobox, preserving its router-driven selection wiring. On a graph with 10,000+ vertex labels, the picker opens and filters instantly.

## Acceptance criteria

- [ ] Data Explorer node-type picker uses the Combobox; route navigation on selection is unchanged
- [ ] Instant open + filter + select on a 10,000-label schema
- [ ] `DataExplorer.test.tsx` exercises the new component and passes
- [ ] `SelectField` and its other callers remain untouched
- [ ] `pnpm checks` and `pnpm test` pass

## Blocked by

- #2087 (Combobox component)

Start with DataExplorer.test.tsx and the existing Data Explorer node-type picker, then read the virtualized Combobox from #2087 and trace the current SelectField router-selection wiring. Done means the picker uses Combobox without changing route navigation, handles a 10,000-label schema responsively, leaves SelectField callers untouched, and passes pnpm checks and pnpm test.

Written by the indexing model from the issue text.